The present invention relates generally to optical devices and, more particularly, to a fiberoptic diffuser providing a generally cylindrical pattern of light emission.
Light-based treatments (i.e., phototherapy) of many kinds are being used or considered for addressing a number of medical ailments. Phototherapy of diseased tissue includes various forms of treatment including photoablation, photodynamic therapy, or photocoagulation. In each of these, control of the treatment outcome relies on control of the dosage of light administered, as well as the dosage of any additional agents such as photosensitizers used in conjunction with the therapeutic light.
Photodynamic therapy (PDT) is an evolving treatment that employs the interaction between photoactive drugs and light of an appropriate wavelength to destroy diseased or malignant tissue. During a PDT procedure, one or more photosensitive molecules are administered within a target tissue of a patient and are then illuminated with phototherapeutic light having a wavelength operable for interacting with the photosensitive molecules in such a manner as to produce a photoactivated species of the molecules possessing therapeutic properties. The photoactivated species that are formed either destroy cells or arrest physiological activity in the associated diseased tissue thereby effecting a treatment of the target tissue.
In PDT procedures, as well as in certain other biomedical applications, optical waveguides (referred to herein as xe2x80x9coptical fibersxe2x80x9d) are used to deliver the therapeutic light energy to internal areas of the human body not readily accessed directly by the light source. In a number of these medical applications, it is necessary to deliver a uniform, cylindrical pattern of light as in the irradiation of a cylindrical area of a blood vessel. Optical fibers used in such therapies typically consist of an inner core having one index of refraction, surrounded by a cladding having a slightly lower index of refraction. Both the core and cladding may be comprised of either an optical glass or polymeric material (such as plastic). Light propagates down the optical fiber by means of total internal reflection at the interface between the inner core and the cladding. The optical fiber is terminated at its distal end with a diffuser having an irradiance distribution appropriate to the particular treatment protocol. An outer protective jacket often covers the optical fiber. Alternatively, light can be delivered into the body using an optical waveguide that consists of a core region only and the waveguiding effect is provided by the interface between the core and the surrounding medium. This type of optical waveguide will also be referred to herein as an optical fiber.
There are various methods used to produce the desired output profiles from interstitial to intraluminal uses. One such device consists of a terminating optical fiber with an attachment on its distal end that forms the diffusing section of the device. Such devices include those described in Dorion et al. U.S. Pat. No. 5,196,005 and Lundahl U.S. Pat. No. 5,303,324. Another type of device consists of an optical fiber with is modified on the distal end. For example, in Fujii et al., Light Scattering Properties of a Rough-ended Optical Fiber, Optics and Laser Technology, February 1984, a process for creating uniform wide-angle irradiation of a laser beam by chemically roughening the output end of a glass fiber is disclosed. In similar processes, the glass core of an optical fiber is stripped by removing the jacket and cladding and then chemically etching the core to distribute the light into layers containing scattering particles to create a uniform cylindrical pattern.
One current approach to diffuser construction is to diffuse scattering elements in a clear material such as epoxy, often with a density gradient of scattering elements to achieve an irradiance pattern that is uniform along the length of the diffuser. One drawback of this approach is that the diffuser is constructed separately and then attached to the end of the fiber resulting in a difficult manufacturing process. Another drawback is that it is difficult to shape the irradiance pattern significantly because it is difficult to arrange the scattering elements in a systematic manner. Further, this technique often results in a fiber optic diffuser with a maximum diameter that is greater than the diameter of the fiber.
Another current approach to diffuser construction is to modify the fiber itself to prevent the total internal reflection of light at the core-cladding interface. There are several ways this is accomplished. One way is to choose a ratio of the indices of refraction between the outer cladding and the core region of the optical fiber so that internal reflection within the core region is substantially less than total. This causes light to radiate outward through the side of the core region and to emerge through (a preferably transparent) cladding. Another way is to alter the interface between the fiber optic core and cladding to increase side radiation. Texturing the outer surface of the core region to provide a ground glass effect is one method commonly used. Another is to position or embed light scattering elements such as tiny particles at the surface of the fiber optic core near the interface with the cladding. Light scattering particles can also be imbedded throughout the cladding to enhance the side delivery of radiation. Yet another approach is to melt or otherwise deform the distal end of the fiber to reduce the waveguiding effect and thereby allow light to be emitted along the deformed region.
Current approaches that modify the fiber itself have only a limited capability to tailor the irradiance distribution. Diffusers which rely on mechanical alteration of the core-to-cladding interface or use a deformed distal end also have the drawback of potentially weakening the mechanical properties of the fiber.
Accordingly, there is a continuing need for an improved optical light diffuser that provides a generally cylindrical pattern of light emission. Desirably, the optical light diffuser would be fabricated relatively readily and would be reliable in operation. In addition, length of the cylindrical pattern of light emanating from the improved optical light diffuser would be varied by facile variation of the manufacturing process.
The present invention provides an economical and easily manufactured optical light diffuser that generates a generally cylindrical pattern of light emission that may be used in various medical applications, such as photodynamic and photochemical treatments requiring uniform irradiation of internal tissues.
In accordance with the present invention, an optical light diffuser, which can generate a generally cylindrical patter of light emission, is provided. The optical light diffuser preferably consists of an optical fiber having a proximal end for connection with an optical light source and a distal end, gradually tapered and preferably terminating in a bullet-shaped tip. The surface of the fiber at the distal end is mechanically abraded in a manner that allows light to escape uniformly over the desired length of the diffuser forming a generally tailored cylindrical pattern of diffuse light.